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1980 450sl - My "learn how to work on cars" car
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Alright, here goes. I am trying to figure out what is going on with the drivers side door locks in my 1980 450sl. When I decided to look at this, I thought I was simply going to be looking for a broken vacuum line or whatnot in the actuator, but now after looking at it for a little bit, I’m not exactly sure what the problem may be or if it’s purely vacuum, purely mechanical, or both. I will try my best to explain what is going on, so hopefully someone can help me out. Let me start off with what I know so far:

1) The door doesn’t seem to lock or unlock with the key. I always leave it unlocked anyways, so I’ve never had it functioning properly
2) The black lock lever (number 1 in the picture) has always stuck out a little bit like this. When I try to press it in all the way, I can’t get it to go in.
a. I am thinking this is because of vacuum in the actuator (3 in the picture). When I manually pull down on the connector between the actuator and the actual door catch, I can hear it release air
3) The lever (number 2 in the picture) was screwed in very tight. Almost so I couldn’t even manually get it to rotate

So I guess there are a lot of potential issues here, and I’m trying to figure out how to narrow it down and a) get the lock working and b) get the vacuum to work properly. Part of the problem is that I am not sure what position the vacuum actuator is in (if it is a locked position or an open position), so it’s hard for me to test different situations.

Are there certain things I can test for to figure out what the state of the door is, and then go and fix it to what it should be? What if I were to disconnect everything and kind of just re-assemble it to a certain state (either locked or unlocked) so I can go from there?

Any thoughts or advice would be greatly appreciated. Thanks!
 

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2010 Mercury Milan Hybrid, 1993 BMW 325i convertible
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6,077 Posts
First things first:

All the links you're talking about should move freely. If they don't, some ham-fisted idiot has played where he shouldn't have.

The black lever should go flush with and parallel to the door for locked. The position it's in now is unlocked.

The master vacuum switch is a little fiddly to get adjusted properly. The place where the screws mount should be elongated, so you can move it up and down. The manual or CD described the adjusting procedure for the different types of vacuum switches out there.

But, seriously, since you've gotten this far I'd just replace it (the master vacuum switch). It has o-rings that dry up and leak vacuum. The cost is minimal, and you've already got the labor done. Just replace it.
 

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1980 450SL & 1988 560SL
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1,667 Posts
I had the same problem with my pass side door. Where the rod goes to the vacuum pod connects to the door mech, there should be TWO spring clips to pop the rod for lock or unlock. See if you have only one. If it breaks, it will just fall into the door. Or take a pic and post and I will see if it is there. I replaced mine with a spare out of my junk car and all is well since.
 

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1998 SL500, 1959 220S, 1970 280SL
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777 Posts
Remember that the operation of the driver's lock is completely mechanical. The rod from the lock moves the vacuum switch so that it applies vacuum to either the lock or unlock side for the pass. door and other elements depending on which way the key is turned.

So as previously noted, you need to be sure that all parts move freely. Note that the inside handle won't move unless the door is shut (to prevent locking yourself out). You may have a lock worn so badly that it won't lock/unlock with the key.
 

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'77 MB 450SLC door locks

My doors will lock from the inside and outside and remain locked. The problem is in unlocking them. Neither of them will unlock when the door is shut, but will do so when open. Any leads?
Thanks, G
 
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